In electrochemical processes it is essential to ensure a uniform distribution of the current over the electrode surface. That uniform distribution is influenced by the throwing power of the electrolyte and by the homogeneity of the electrodes. The throwing power will increase with the surface area on which the current flow lines are incident on the counterelectrode. While an inadequate throwing power can be compensated by an increase of the interelectrode distance, this will increase the voltage drop across the cell.
If inhomogeneities are present in the surface of the electrode, the flow of current will result in local distortions. For this reason the interelectrode distance i.e., the distance between the anode and the cathode, is of great importance. In membrane electrolytic cells having a membrane and producing gases, such as chlorine, oxygen, hydrogen, it is difficult to maintain or adjust a small interelectrode distance and the gas bubbles cannot escape as quickly as is required if the interelectrode distance is small.
Any gas present in the electrolyte between the electrode will reduce the electrical conductivity of the electrolyte so that the power consumption will be increased. In addition, microscopic distortions of the surface of the electrode may be caused by the electric current. The evolution of gas also gives rise to turbulence in the electrolyte. A turbulent motion of the electrolyte has the disadvantage that the membrane is subjected to intense mechanical stress. In order to avoid an accelerated destruction of the membrane it is generally necessary to restrict the height of the electrodes, to select a considerable distance between the electrodes of the cell, and to limit the electric current density although this will adversely affect the energy efficiency of the electrolytic cell and its productivity.
To reduce the disadvantages of electrolytic cells having membranes and vertically extending electrodes it is usual to employ electrodes having openings for the escape of the reaction gases. Such electrodes may consist of perforated electrodes, wire mesh or expanded metal. The disadvantages reside, inter alia, in a smaller active surface area, inadequate stability and loss of high-grade coating material on the rear of the electrode.
It has been proposed in German Patent document No. 2,059,868 to provide in gas-forming diaphragm cells having vertically extending electrodes, a plate electrode which consists of several plates having surfaces for guiding the escaping gas which has been formed.
The inclination of the guiding plate inevitably resulted in different distances from the active surface to the counter electrode. French Pat. No. 1,028,153 discloses an electrolyzer in which the electrodes are parallel and have the smallest possible spacing. The known electrodes consist of one or more strips which define horizontal openings formed by an angled portions of the strips and opposing the escape of gas with the smallest possible resistance. The angled portions extend away from the counter-electrode so that the active surface area is not appreciably reduced. A similar electrode arrangement is known from German Pat. No. 453,750. These electrodes are formed with cuts, which permit portions of any desired configuration to be bent out so that they extend away from the counterelectrode.
While such electrodes, particularly cathodes, have been known for more than 30 years, they have not been commercially exploited, but perforated sheet metal, expanded metal or similar materials are still employed.